The road network is the main artery within the city structure, which requires designing of routes and classification within the standards. Hence, the importance of this chapter, which will focus on the standards and design elements of the engineering design of road in terms of road type system, functional classification system, traffic volume system, number of traffic lane system, road width design, side slopes and elevations of road layers, super elevation, design speed, overtaking and stopping sight distance, longitudinal and cross sections of the road path, design elements of horizontal and vertical curves, and intersections. The Civil 3D Land Desktop, GIS programs, and remote sensing technology will be used to design the path of major highway linking two urban areas in Mosul (Northern Iraq), which will be considered a case study. The path of the road and its elements will be designed according to special criteria that are compatible with the topography and nature of the area. The geometric data of the road will then be exported with all the design elements to the GIS program to build an integrated road database. The database is capable of spatial analysis and connectivity with other parts of the road network in the city.
- spatial database
- road design
- Civil 3D
Transport has now become an important factor in determining the housing and workplaces of the largest segment of society. Transport has thus become an essential element in determining land uses; it is not affected by land uses only but affects them. The transport activities directly or indirectly lead to the transfer of civilization and civil landmarks to the farthest points in the country, open to human societies’ paths to flow of science and knowledge, improve the health and social conditions and enjoy the joys of life and nature, and expand the perceptions of these communities and openness to ensure stability and development. In light of this, the efficiency of the transport system and roads requires continuous planning and design for the road, especially with respect to the design of engineering elements of the road, in order to provide the movement of society and maintenance at an acceptable level.
The engineering design of the road is defined as the process of finding the engineering dimensions of each road and arranging the visual elements of the road such as the path, distances of sight and passing, width, slopes, curves, super elevation, and other engineering characteristics. The horizontal and vertical design elements of the road are considered the most important elements of road design because their minimum limits are the basic for the design speed and the ruling slopes.
The horizontal and vertical roads’ elements, the configuration of road path and grade affects safe operating speeds, and sight and passing distances for highway and roads’ capacity establish the general character of a highway, more than any other design consideration. These components will significantly affect the safety, operational efficiency, and aesthetics of the highway.
Therefore, this chapter will focus on the design of the main elements of a road linking the city of Mosul and Makhmour (Northern Iraq) district south of Mosul. The surveying data was prepared by the Ministry of Municipalities for the proposed route of this road using a differential GPS device.
These surveys are a 900-m strip survey of the proposed route of the Mosul-Makhmour highway with a length of up to 20 km. Field surveying data will be used to prepare a geometric design for the proposed road linking for the two regions by using AutoCAD Civil 3D Land Desktop program and in accordance with international standards.
Initially, a path was proposed for this road depending on spatial analysis by GIS program to get optimum path linking between two areas. The stations, the type of road, the number of its lanes, its dimensions, its horizontal and vertical elements, and the slopes were defined according to the main design criteria of urban roads. The results were illustrated by longitudinal and cross-sectional plots showing the changes in the natural shape of the ground and all the elements of the horizontal and vertical curves of the road. After which, the volume of the earthworks was calculated for excavation and burial. Thus, a road connecting two urban areas was achieved in a manner that does not cause accidents and achieves the smooth flow of vehicles by making all elements of the road consistent with the expectations of drivers to avoid sudden changes in design specifications. Finally, all the designed road data were exported to the GIS program to build an integrated database for this road that can be linked to the rest of the city network, as well as all spatial analyses and network analyses.
2. Transportation planning
Transport is an important part of the planning process for cities and regions. Every planning activity, whether land uses, work centers, cultural, marketing, or leisure activities, depends in one way or another on transportation. The transport and traffic sector is considered an important sector in economic development, and this is reflected in the high expenses allocated to the development of this sector, which in Iraq up to 20% of the allocations of annual investment plans .
Transport planning is a structured approach to understanding traffic and transport characteristics. It aims to achieve an efficient and appropriate system that meets the current and future requirements of the community. We can define a number of objectives for this process :
Provide the most appropriate type of transport system according to the available potentials.
Developing and increasing the efficiency of economic activity by reducing transport costs.
Development of an integrated system of transport routes.
Know how and when to improve the old road or build new roads according to future requirements.
Optimal expenditures through the implementation of program cost and benefits for road projects to the general community.
Development of programs and techniques for further urban and regional development.
Reducing traffic accidents.
To preserve and improve the environment.
Also designed to design road networks according to planning standards, the most important of which are as follows :
The network hierarchy, which is related to the functional classification of the different ways of fast, primary, and secondary traffic.
The network serves land use (residential, industrial, commercial, cultural, etc.) in a good way, providing easy access to parts of the city or regions.
The large and equivalent link between the city’s internal network and the regional road network.
Network service for the gradual development of the city.
Avoid traffic jams that may occur at intersections by creating junctions at levels or any other planning solutions.
3. Road network classification systems
The systems adopted in the road network classification classify the network into four sections according to the following concepts :
Road location systems and neighborhoods: The road is classified according to its location according to the following concepts: the type of use of the road, the date of construction of the road, the uses of the ground surrounding the road, topography of the area of the road, and nature of the area.
Road engineering design system: These systems are based on the engineering classification of the road network according to the following systems, number of road lanes, system dividing the road, and switching systems from one road to another.
Road administration systems: These systems work on road management according to the following concepts, road planning according to levels, road paving systems and maintenance, road ownership systems, and type of tiling material systems.
Vehicle traffic systems: The road network is classified according to the movement of vehicles and their relation to the type of vehicle, according to the following, traffic volume of the road, purpose of the trip, type of vehicle using the road, and the roads’ functional classification.
4. Classification of road network according to the criteria of capacity and rank
Free streets: These streets are designed for the purpose of speeding and long distances in international and regional trips, with a capacity of between 1800 and 2000 vehicles/h, with lanes ranging from 4 to 8 lanes, at a speed of operation ranging from 80 to 120 km/h.
Express streets: The streets are meant to serve the largest number of citizens, high speed, long distances for regional trips, a capacity of between 1400 and 1800 vehicles/h, and lanes of 4–8 lanes, with a speed of operation ranging from 60 to 80 km/h.
Arterial streets: The streets with medium-distance urban trips, easy access between parts of the city and a capacity of 800–1200 km/h, with a speed of 40–60 km/h.
Collected streets: These streets mean short urban trips, easy access between the city, and a capacity of 600–900 vehicles/h, with a speed of 30–50 km/h.
Local streets: For short transport service, at a low speed of 20–30 km/h, with a capacity of 500–700 vehicles/h .
5. Functional classification of urban roads
The importance of functional classification is determined by which the role of each road is defined for the traffic and transport service. The degrees of urban roads vary according to the areas they serve, whether residential, commercial, residential-commercial, etc. and also according to the total movement that will be generated from those areas served. Classification of roads in urban planning can be summarized as follows [6, 7, 8]:
Major urban roads: These roads link the main centers of activity in urban areas. They are connected to the regional network and take the largest traffic load in the urban area. These roads have width about 40 m or more.
Secondary urban roads: These roads collect the vehicles from the main roads and distribute them to the degree of lower roads, and their widths are about (16–25 m).
Urban roads of the third degree (local): Collecting vehicles from the residential areas and areas of activity to the highest road degree and carrying the least amount of traffic in the network and is the lowest degree in the hierarchy of the road network and its widths about (12–16 m).
The design characteristics of the road must be commensurate with the design speed chosen and expected for environmental and terrain conditions, and the designer should choose the appropriate design speed based on the planned road degree, terrain characteristics, traffic volume, and economic considerations. Note Table 1.
|Degrees||Minimum speed (km/h)||The desired speed (km/h)|
|General arterial road||80||100|
6. Highway capacity and level of service
The capacity of the road is the maximum number of vehicles expected to pass over a particular part of a lane or road during a given period of time under the prevailing traffic conditions.
Service level is the qualitative measurement of the effect of a number of factors such as operating speed, travel time, traffic failures and freedom of maneuver, and crossing, driving safety, comfort, road suitability, and operating costs for the service provided by the road to its users. Table 2 shows the characteristics of the service level according to the type of road [9, 10].
|The level of service||Urban arterial||Two lanes road|
|A||The average speed is about 90% of the speed of free flow. Delay at intersections with traffic signals is minimal||The average speed of the road is 93 km/h or greater. Most of the crossings are carried out without delay. In the ideal case, the traffic volume is 420 vehicles/h for both directions|
|B||The average speed of traffic decreases due to the delay in intersections and the impact of vehicles on some of them and about 70% of the speed of traffic. Load factor at 0.1 intersections and peak hour factor 0.8||The average speed of the road is 88 km/h or more. The load coefficient may be up to 0.27. Traffic volume is 750 vehicles/h for both directions|
|C||Travel speed is about 50% of the speed of free flow. Run balanced. Long rows of cars when traffic signals are possible||The average speed of the road is 84 km/h or more. The flow rate in the ideal case is about 43% of the capacitance, with a mean traffic in ideal conditions 1200 vehicles/h in both directions|
|D||Average speed 40% of free flow rate. The flow rate is unbalanced, and delays at intersections may be comprehensive||The average speed is 80 km/h. The flow rate is about 64% of the capacity, with continuity in the imposition of overflow and flow of approximately 1800 vehicles/h for both directions|
|E||Speed of flow is 33% of free flow speed, volume at capacity, and flow is not balanced. The coefficient of load at intersections (0.7–1.0). The peak hour factor is 0.95||The average flow rate is about 72 km/h. The flow rate in ideal conditions is 2800 vehicles/h; level E may not be accessible as the operation is converted from service level D to F directly|
|F||The average speed of traffic between 25 and 33% of the speed of free flow, high delay times at the branches of intersections||The operating speed is less than 72 km/h, and the traffic are overcrowded and constrained with unexpected characteristics, volume less than 2000 vehicles/h in both directions|
7. Specifications and determinants of roads’ design and general criteria
7.1 Stopping sight distance (SSD)
The distance traveled by the vehicle from the instant the driver sights an object necessitating a stop to the instant the brakes are applied and the distance required to stop the vehicle from the instant brake application begin or defined as the sum of distances from when the driver decides to apply the break until the car stop, as in Eq. (1):
where (SSD) is the stopping sight distance in m, (V) is the initial speed (kph), (a) is the rate of deceleration (3.4 m/S2), and (t) is the Brake reaction time, which is assumed to be 2.5 seconds by AASHTO .
Table 3 can illustrate the stopping sight distance and its relation to the design speed, brake reaction distance, and braking distance on level. Table 4 illustrates increment of the stopping sight distance and its relation to the design speed and brake in state of slope directed down [12, 13, 14].
|Design speed (Km/h)||Brake reaction distance (m)||Braking distance on level (m)||Stopping sight distance|
|Calculated (m)||Design (m)|
|Design speed (km\h)||Increase the stopping sight distance in state of downslope (m)|
7.2 Passing sight distance (PSD)
It represents enough free distance of traffic so that the driver can see the driver in front of him to be able to complete the process of circumventing without touching the car that passes without being intercepted by any counter vehicle may appear after the start of the bypass and then return to the right warm easily after the overtaking process. PSD is designed for two-lane highway as in Table 5 which illustrate passing sight distance with respect to the design speed for passed and passing vehicle .
|Design speed (km/h)||Assumed speed (km/h)||Passing sight distance (m)|
|Passed vehicle||Passing vehicle||From exhibit 3–6||Rounded for design|
7.3 Horizontal planning of the road
The horizontal curve is a part of circular curves, which consist of intersection of two tangents of road. Horizontal curve has four types illustrated in Figure 1. The location and configuration of the horizontal curve are affected by some of the factors as follow :
Physical condition: land uses, earth topography and geophysical conditions, intersection with waterway and man-made barriers.
Environmental circumstances: impacts on the adjacent land use, community-based impacts, and environmentally sensitive areas.
Economics condition: cost of construction, road ownership costs, effects of utility, costs of operating, and maintenance.
Road safety: distance of sight, alignment consistency, considerations of the human factor.
Classification and design considerations of highway: level of service, functional classification, design speed, and standards.
7.4 Vertical planning of the road
Vertical road planning consists of a series of longitudinal tendencies connected to each other by vertical curves (note Figure 2). Vertical planning is governed by a number of factors: safety, terrain, road speed, design speed, horizontal planning, construction cost, vehicle characteristics, and rain drainage. Visibility in all parts of the longitudinal sector must be met with the minimum distance required to stop (not overtaking), according to the design speed corresponding to the roadway. There are general considerations in the vertical planning of the road, which can be summarized as follows [19, 20]:
The goal should be to obtain an easy linear elevation design with gradual changes in line with the type of road or its degree and the nature of the land.
Avoid wavy vertical planning or vertical planning with hidden dips, because it is bad-looking and dangerous. Hidden dips cause accidents in overtaking, fooling the overtaking driver beyond the low, and thinking the road is free of anti-cars. But in the low-depth depressions, such as a longitudinal ripple, there is a lack of reassurance in the driver because it cannot determine the presence or absence of a vehicle likely to be hidden behind the high part. This type of longitudinal layout can be avoided by horizontal curvature or gradual change of slopes at light rates, possibly by increasing cutting and filling.
The longitudinal refraction bending planning should be avoided (two vertical curves in the same direction separated by a short tangent), especially in concave curves where the complete view of the two curves is not acceptable.
It is preferable for long slopes to have steep slopes at the bottom, and then the slope falls close to the top, or the continuous gradient is reduced by the introducing short distances where the slope is less than that of a regular full slope. This is especially relevant for low-design speed road conditions.
K values can be used to compute the length of vertical curve for the crest and sag vertical curves. And vertical curve should have minimum length equal to three times the design speed.
SSD in most cases will be used for the length of vertical design, but for trucks it is not necessary because the driver of the truck is able to see farther than the passenger car. So, the SSD for trucks and passenger cars is balance.
|Design speed (km/h)||Stopping sight distance (m)||Rate of vertical curvature (K)|
|Design speed (km/h)||Passing sight distance (m)||Rate of vertical curvature (K) design|
7.5 Super elevation
Super elevation allows the car to travel across a curve safely and at a higher speed than is possible with the natural crown section. The overall super elevation rate increases with speed and a sharper curvature (note Figure 3). Table 8 can illustrate the maximum lateral lifting value of super elevation .
|Degree of the road||Maximum side lifting value of the road is desirable (m/m)||Maximum lateral lifting value is absolute (m/m)|
where Rv is the vehicle’s traveled path radius, Ff is the force of side frictional, FC is the centripetal force, Wp is the weight of vehicle parallel to the road path surface, W is the vehicle weight, Wn is the vehicle weight normal to the road path surface, Fcn is the gravitational force that works naturally on the road surface, e is the number of vertical of rise per one horizontal station (100 m), and α is the incline angle .
7.6 Side slope of cut and fill
Side slopes are designed to ensure the stability of the road and to provide the opportunity to secure cars out of control. Table 9 shows the relationship between the topography type and the height of the cutting or the filling, and the maximum side slope desired in the roads for the filling slope less than or equal to (2:1) depends on soil analysis [24, 25].
|Height (m)||Earth work||Plan||Wavy||Mountainous|
|Desired||Max slop||Desired||Max slop||Desired||Max slop|
8. Spatial data of study area and method of processing
For the purpose of designing the proposed road elements of the study area between Mosul and Makhmour, the spatial data of the study area were obtained from the Ministry of Municipalities of Mosul City.
The spatial data is the field survey data of the route of the road, completed by a team of engineers from the Ministry of Municipalities. The survey data was conducted in the form of a strip width 900 m around the proposed route. A 900-m width was selected to cover all the places that the road path might pass, because the path was selected roughly, not accurately. The length of the strip survey is 20 km to connect the two urban areas.
The survey data contains a set of point coordinates (3626 points) observed with a high-precision equipment (Leica viva GS15). The coordinates’ projection was WGS84-UTM-Zone38N. These data is an unprocessed raw data, unrelated to each other, and contains many coordinates that may not be connected to the pathway. For the purpose of processing these data and linking it together, adjusting the system of coordinates, adjusting the elevations, and creating a digital elevation model for the region, the Civil 3D Land Desktop program will be used to process this data and then export it to the GIS program.
Spatial analysis will be used in the GIS program to select the optimal path that connects the two study areas based on spatial data. The optimal path for the proposed road will be chosen according to planning and design criteria. This path will be exported to the Civil 3D program again to identify the rest of the design elements of the road.
In the Civil 3D program, all the design elements of the road will be defined according to the AASHTO standards, leading to the final stage where the road contains an integrated database ready for implementation.
9. Methodological steps for designing road elements using Civil 3D Land Desktop and GIS software
In order to define the proposed road path and all its horizontal and vertical and design elements, these points will be used in the definition and design of road elements according to the following methodological steps:
The civil 3D land desktop program has been configured to be in meter units, 1:1000 horizontal scale and 1:50 vertical scale, UTM, WGS 84 Datum as Figure 4.
The survey points were imported within the program and arranged and modified (point number, coordinates values, elevations) to be ready for the purpose of design road elements, as in Figure 5. Constructing a surface triangulated irregular network (TIN) and connecting the points’ coordinates for the purpose of deriving the elevations of the road depending on it, as in Figure 6. The TIN surface is then exported to GIS as digital elevation model (DEM).
The Geographic Information system (GIS) program was used to select the best route for the road connecting the city of Makhmour with the city of Mosul, as in Figure 7 which shows the sequence of steps to choose the path. The network of TIN has been reclassified according to the elevation values, so that the road passes from the flat areas as much as possible, as the land on which the road passes has steep slopes. The land use layer has been reclassified so as not to cross the road with any unwanted land use. The best and shortest route between the two urban areas was then chosen. The length of the best selected path was 18210.88 m. Its alignment, stations, width, and number of lanes were defined and exported to the civil 3D.
ASHTO standards were adopted in the design of horizontal elements of the proposed highway. These design elements were defined to the Civil 3D as follows:
The design speed = 100 km/h.
Maximum longitudinal slope = 3%.
Maximum side slope = 4/1.
Stopping sight distance SSD = 185 m.
Supper elevation = 4%.
Break reaction distance = 60 m.
Break distance on level = 115 m.
For concave and convex vertical curves (sag and crest), SSD = 185 m, PSD = 670 m, K = 45.
Minimum length of vertical curve = 700 m.
The level of service was A, the number of lane 2 was with two direction, the chosen width was 12 m per lane, and the traffic volume was 420 vehicles/h in both directions.
The design elements for the horizontal curves were illustrated as in Figures 8 and 9. Where the highway contained four horizontal curves designed according to the design standards. Figure 10 can illustrate the proposed path of road after adding the stations. While, Figure 11 illustrate the definition of the design velocity of horizontal curves.
The construction line (formation level), which represents the final level of the road, has been defined so that it achieves the lowest proportion of cuttings and fill in the earthworks and with the lowest vertical curves and as in Figure 13, which illustrates the elements of vertical curves and stations of PVC, PVI, and PVT through the table stations, as well as the levels of these stations, their slopes, and the length of their vertical curves, and the type of curve. Figures 14 and 15 illustrate the longitudinal section after adding the line of construction and vertical curves.
The cross sections of the proposed road were generated and designed according to the criteria that correspond to the cross sections of the reality of the case (width of the total road 24 m, shoulder length 1 m, side slope 1/2, supper elevation 4%, the thickness of the tiling was defined as 10 cm, thickness of the subbase 15 cm). Note Figure 16 which illustrates the forms of some of cross sections.
Calculated volume of the earth works in a way of prismoidal formula as shown in Table 10, which shows the volume of cut and fill for each station of the proposed road. These data of volume were exported from Civil 3D to GIS as attribute table.
The length of the proposed road was 18210.88 m according to the data of the Ministry of Municipalities, 24 m width with two corridors, and the coordinates system was UTM.WGS 1984 and Zone 38N.
The TIN is the basis of the accuracy of the roads’ coordinates, because it is observed with accurate GPS devices.
All horizontal and vertical road elements are defined through the CIVIL 3D program, facilitating and accelerating the design process in accordance with international standards.
Four horizontal curves and three vertical curves were proposed for the proposed road, according to the topography of the earth, which required this number of curves.
The design of the roads using Civil 3D and GIS in all its components makes the design process highly efficient through the speed of time, little effort, and low cost.
Civil 3D has all the international standards used in road design and has all the tools that can easily define all design elements for roads and export it to GIS.
The program provides us with longitudinal and cross sections that show the change in ground and construction line levels very accurately, which facilitates the process of proposing tiling and cladding levels.
The volume calculated by using the program is very precise. The earthwork produced by the pieces can be used to bury the areas that need to be buried. The construction line chosen to represent the proposed road level was chosen at the same depth as the depth of the burial.
The road data exported to the GIS program has created an integrated road database. This database can be performed on any kind of spatial analysis or network analysis of the roads within the environment of the GIS.
The authors would like to thank Mustansiriyah University (